1. Field of the Invention
This invention relates generally to the removal of a dielectric coating from the surface of a material and, more particularly, to the removal of an insulating coating from a conducting material by means of a plasma created by a focused laser beam.
2. Discussion of the Related Art
The removal of dielectric coatings from conducting materials can be difficult to achieve. Indeed, dielectric coatings are selected to adhere strongly to the coated material to minimize the inadvertent removal of coatings. A more stringent requirement is that the dielectric coating removal must be sufficiently complete to provide a surface on the conductor that will permit electrical coupling by another conducting material. Abrasive methods are frequently time-consuming and can cause mechanical damage to conducting elements. In addition, caution must be exercised in the use of the abrasive techniques. Otherwise, the removal of dielectric coating can fall outside the desired physical boundary of the conducting material for the coating removal.
Another technique for the removal of an insulating or dielectric coating is the use of solvents, acids or other chemical agents. This technique has become less desirable as subsequent, and still increasing, restrictions on the disposal of toxic materials have resulted from identification of cumulative environmental problems caused by toxic waste disposal. Thus, the use of chemical removal of insulating coatings has become increasingly expensive and frequently results in the dedication of unacceptable amount of resources in an area peripheral to the main business function.
Another technique for the removal of an insulating coating has been the use of radiation heating for the vaporization of the coating. This technique suffers from two problems. First, the impinging radiation must fall within an absorption band of the dielectric coating material to provide efficient heating of the insulation to remove it from the coated material. In addition, the insulating coating is typically deposited on a conducting material, and the electrically conducting material being a good thermal conductor, provides a heat dissipation mechanism in the region of the insulating material in close proximity to the conducting material and can leave residual materials that compromise the ability to couple electrically to other conducting materials. These problems can be overcome with intense sources of radiation. However, when the insulating coating becomes less than half a wavelength of the impinging radiation, the conducting material supporting the coating imposes a boundary condition for the radiation that limits the power density that can be concentrated in the vicinity of the conductor.
Therefore a need has been felt for apparatus and method of removal of the insulating coating with well-defined physical boundaries which do not leave residual insulating material and which do not produce damage to the conducting material supporting the dielectric material.